The project deals with the patterns of proliferation of tumor cells and the effects of antitumor agents thereon. In the tumor model under investigation, the slowly growing autogenous methylcholantherene-induced sarcoma of the rat, the cells move back and forth between the proliferative and non-proliferative compartments. Appreciable numbers of cells spend many days in G10 and G20. Of particular interest are the movements of cells between the proliferative and non-proliferative pools during the administration of antitumor drugs and their behavior after withdrawal of the drugs. The design of these studies is intended to simulate that of the solid human cancer. Projected experiments examine the effects of currently employed chemotherapeutic agents upon these kinetic parameters. The objective is more effective use of these compounds in the control of tumor growth.